Multi-hop ramp feed for wire-grid lens antenna



Sept. 1969 R. 1.. TANNER ET AL 3,465,343

MULTI-HOP RAMP FEED FOR WIRE-GRID LENS ANTENNA Filed oct. 11, 1965 2Sheets-Sheet 2 I E f/x7/yzA/ro/es DWA/w .Jo/vt's I 6' FRANK B, HAP/W5rm.

EL/GE/VE D. SHARP QOBERT L. TAIVIVEI? United States Patent sota FiledOct. 11, 1965, Ser. No. 494,659 Int. Cl. H01q 11/06, 9/06 US. Cl.343-736 3 Claims ABSTRACT OF THE DISCLOSURE A feed arrangement isprovided for a wire grid lens antenna. The antenna comprises a pair ofspaced overlying conductive wire grids substantially in the form of twocircular concave discs spaced from one another. The feed arrangement forsaid antenna, in accordance with this invention, comprises at least oneconductor which makes multiple transitions or multiple hops between theupper and lower grids. A phase inverting network is connected at eachreversal between upper and lower discs of the ramp feed conductors sothat all the current of the several sections radiates in phase in onedirection. A transmitter is provided at one end of these feed conductorsand a terminating network is employed at the other end.

This invention relates to antennas of the type known as wire-grid lensantennas and, more particularly, to an improved arrangement for feedingsaid antennas.

In an application for patent, Ser. No. 175,369, and also in applicationSer. No. 175,374, both of which were filed on Feb. 23, 1962, and arerespectively entitled Uniform Wire-Grid Lens Antenna and Non-UniformWire- Grid Lens Antenna, and both by Robert L. Tanner, one of theinventors of the present application, there is described and shown awire-grid lens antenna of a type with which the present invention findsits optimal use. A wire-grid lens antenna may be broadly described ascomprising a central lens region surrounded by a horn .region. Both thelens and the horn are made of wire grid mesh. The central lens regioncomprises a pair of spaced overlying conductive wire grids substantiallyin the form of two circular concave discs, with'the lower surface of oneopposing the upper surface of the other. The horn region flaresoutwardly from the disc periphery. Such an antenna has excellentbroadband characteristics for operation over the bands lying within thefrequency range extending from below one to above 1,000 megacycles persecond.

In another application for patent by this inventor, Ser. No. 370,471,filed May 27, 1964, and entitled Lens Feed System, there is described anovel arrangement for feeding a wire-grid lens antenna of the generaltype described, which comprises a transmission line connected to thetransmitter or receiver by an input network at the lower grid element ofthe lens and which extends diagonally upward to couple to the upper lensgrid element through an output network at a predetermined distance fromthe edge of the lens. In order to suppress undesirable side radiation,dipole elements are provided and are excited in phase quadrature withthe ramp element to assist in minimizing or eliminating the undesirableside radiation.

An object of this invention is the provision of a ramp type feed whichminimizes side radiation without using radiating dipoles.

Patented Sept. 2, 1969 Another object of this invention is the provisionof a feed arrangement for an antenna of the general type described whichhas an improved efliciency over the single ramp feed and can give lowside lobes over the bands lying within the frequency range extendingfrom below one to above 1,000 mHz.

Yet another object of the present invention is the provision of a noveland improved feed for a wire-grid lens antenna.

These and other objects of the invention are achieved in an arrangementwherein instead of the feed conductors making a single transition fromthe lower to the upper lens, they make multiple transitions or multiplehops between the lower and upper lenses. A phase inverting network isconnected at each reversal of the ramp feed conductors so that all thecurrent of the several sections radiate in phase in one direction. Aterminating network is employed at the end of the feed.

The novel features that are considered characteristic of this inventionare set forth with particularity in the appended claims. The inventionitself both as to its organization and method of operation, as well asadditional objects and advantages thereof, will best be understood fromthe following description when read in connection with the accompanyingdrawings, in which:

FIGURE 1 is a perspective view of a wire-grid lens of the general typewith which this invention is concerned;

FIGURE 2 is a schematic view of a multihop ramp feed in accordance withthis invention for a wire-grid lens;

FIGURE 3 illustrates how the turn around, or phase inverting point of atwo-hop ramp feed may be moved to optimize the location thereof;

FIGURES 4A and B show various configurations of the ramp conductors,which may be employed for improving the radiation pattern; and

FIGURE 5 is a circuit diagram of an optimized twohop ramp feed for awire-grid lens antenna.

FIGURE 1 is a perspective view of a wire-grid lens antenna of thegeneral type which has been described and claimed in thepreviously-indicated patent'applications by this inventor. The antennahas a center portion 10 which forms a wire-grid lens for azimuthal beamshaping, and a peripheral portion 12 which is the horn or radiatingstructure for elevational beam shaping and for matching the impedancebetween the wire-grid lens 10 and the surrounding space. The radiationstructure 12 is shaped .in the form of a biconical or-radially flaredhorn.

The wire-grid lens 10 includes-an upper wire grid14 and a lower wiregrid 16 spaced in opposite and-overlying relationship by means of aplurality of nonconductivesu'spension or support members 1-8. As apractical matter, the peripheral portion of the upper wire grid 14andthe lower Wire grid 16 may be secured through rim members, such as apair of metal rings 20, 22, respectively which are light in weight andwhich form convenient'conduc'tive terminating support edges.Furthermore, these rings also provide a convenient meanstfor-attachingthe radiating structure 12 thereto. The lens wire grids 14 and 16, are

formed'of composite metallic wires in the form of a mesh structure.

eter of 600 feet and a distance of separation beween the upper and lowerelements of the lens at the center is on the order of 6" and at theouter periphery is on the order of 12 feet. The biconical horn portionextends outwardly still farther from the periphery of the lens portion.The feeds in accordance with this invention are installed at the end ofthe lens portion and may extend from the junction between the lens andthe horn portion for a distance on the order of one-fourth of the lensradius towards the center of the lens. In this region the spacingbetween the grids of the lens is large enough so that the lens elementspresent approximately parallel conducting planes. In an embodiment ofthe invention which are built and operated satisfactorily, thirty-sixfeeds were employed spaced around the lens.

FIGURE 2 is a schematic diagram of a multi-hop ramp feed element for awire-grid lens, in accordance with this invention. It can be used in thelens antenna for either transmission or reception of electrical signals.When used as a transmitting feed, the current, excited by a source 40 atthe input of the feed, travels to the right along the ramp segmentsrespectively 42, 44, 46, and 48, coupling energy into the lens antenna.A phase inverting network respectively 43, 45, and 47 is connected ateach reversal of the slope of the ramp segments so that all currents ofthe several sections or hops radiate in phase toward the right. The rampfeed terminates in a network 50, which as shown in FIGURE is animpedance matching network.

As will be discussed in connection with FIGURE 5, the ramp segments ofthe multi-hop ramp may consist of one or more electrical conductors inparallel, arranged so as to achieve a desired impedance level.

The ramp feed arrangement, which is schematically represented in FIGURE2, has an improved efiiciency over the single ramp feed shown anddescribed in the application by Robert L. Tanner et al., Ser. No.370,471, which has been previously mentioned. The purpose of the phaseinverting networks which are provided is to cause the waves from boththe downward directed ramp segments and the upward directed rampsegments to be added in phase toward the right. Improved couplingefficiency results from the fact that the vertical displacement of theramp-centroid for a given radial distance along the ramp is increased inproportion to the number of hops employed. FIGURE 2 illustrates afour-hop ramp. The same concept can be applied to feeds having two,three, or even five hops. Also, the phase inverting networks can besimple phase inverting transformers or can be transformers plus moregeneral networks.

While a substantial improvement is derived in going 0 [from a simplesingle ramp feed to a two-hop ramp feed,

the additional improvement gained by using more than -two hops ismarginal and is not believed to justify the ina limitation upon theinvention since the concepts to be developed are also applicable to morethan two hops.

Another parameter at the disposal of a designer in connectionwith themulti-hop ramp is the location of the turn around or phase invertingpoint. This is illustrated in FIGURE 3 which shows three possiblelocations for .the phase inverting transformer in a two-hop ramp. In-

vestigation of many configurations, each optimized with respect to theterminating impedance and other factors, indicated that the best overallperformance is obtainable when a phase inverting transformer is placedat a point approximately one-third of the radial distance between thefeed end 40 and the terminating network end of 4A, the conductor 42 isbent so that the second half thereof is closer to the upper lens 14. Theconductor 44 is bent so that the second half thereof is closer to thelower lens 16. In FIGURE 4B, the conductor 42 remains bent as in FIGURE4A. However, the conductor 44 is now bent so that the first half iscloser to the upper lens 14. Since the source strength per unit lengthof the ramp is proportional to the vertical displacement of the ramp perunit of radial distance, the illumination function is controlled byplacing the ramp conductor along a path Where its slope varies. Thearrangement shown in FIGURE 4B, which tends to concentrate the radiationfrom the twohop ramp near its beginning and near its end proves to givethe best patterns of any of the configurations investigated.

FIGURE 5 is a circuit diagram of the ramp feed in accordance with thisinvention, which shows the preferred slope of the ramp feed segments.These ramp feed segments 42, 44 represent one or more electricalconductors in parallel arranged so as to achieve a desired impedancelevel. In general, the impedance is lowered by adding conductors or byincreasing the spacing between the conductors. The preferred phaseinverting structure 43 comprises a phase inverting transformer. Theterminating network 50 comprises a resistor connected in series with theramp segment 44 and to the lower lens element, and across which there isconnected an inductance 50L and a capacitance 500. If the terminatingnetwork includes a resistance equal to the characteristic impedance ofthe ramp segments, the feed energy that is not coupled into the lensantenna will be entirely absorbed by the terminating resistance.However, if the resistance is not so chosen, and other circuit elementsare added to the terminating network, such as the inductance 50L andcapacitance 50C as shown in FIGURE 4, then some of the feed energy isreflected and can be controlled so as to reduce the side lobe radiationfrom the lens antenna.

The embodiment of the invention which is preferred is shown in FIGURE 5.The phase inverting transformer is placed at a point approximatelyone-third of the radial distance (L) between the feed end and theterminating end of the ramp. The ramp segment 42 has the conductorsthereof rise from the source 40 to a point 52 threequarters of thedistance between the upper and lower lens element which is also locatedat a point one-sixth of the distance L, which is the distance betweenbeginning and end of the ramp feed. From this point, the ramp segmentconductors extend at a smaller slope to the phase inverting transformer43. A point 54 marks the location along the conductors of the rampsegment 44 at which the slope thereof to the terminating resistanceincreases. This point is determined as being at a distance two-thirds Lor two-thirds of the distance between the beginning and termination ofthe ramp feed, and three-quarters of the distance H2 which is thespacing between the upper and lower lens elements at this location.

There has accordingly been described and shown hereinabove a novel,useful and improved arrangement for feeding a wire-grid lens antenna.

What is claimed is:

1. In a wire-grid lens antenna of the type wherein said wire-grid lenscomprises an upper and a lower lens element each being made of wire gridand each having substantially the shape of a disc, both resembling twospaced opposite saucers, said upper and lower elements being spaced apredetermined distance from one another,

an improved feeding structure comprising:

first conductor means extending from an edge of one of said two spacedlens elements radially inward to a first location at the surface of theother of said two elements,

a second conductor means extending from said first location radiallyinward to a second location at the surface of said one of said two lenselements, said first location being placed at onethird the distancebetween said edge and said second location,

phase inverting means located at said first location for transferringelectrical energy between said first and second conductors, and

terminating network means at said second location connected between saidsecond conductor and said lower wire-grid lens element.

2. Apparatus as recited in claim 1 wherein said first conductor meansextend from said one edge to a point which is substantially one-sixth ofthe distance between said one edge and said second location andthree-quarters of the distance between said upper and lower lens elementat that point, and said first conductor means extends from said point tosaid phase inverting network, and said second conductor means extendsfrom said phase inverting network to a second point which is positionedat a location two-thirds of the distance between said edge and saidsecond location, and which is three-quarters of the distance betweensaid upper and lower lens element at said second point.

3. In a wire-grid lens antenna of the type wherein said wire-grid lenscomprises an upper and lower lens element, each being made of wire gridand each having substantially the shape of a disc, both resembling twospaced, opposite saucers, said upper and lower elements being spaced :apredetermined distance from one another, an improved feeding structurecomprising:

conductor means extending from an edge of one of said two spaced lenselements radially inwardly and making more than one transition betweenthe upper and lower lens elements, the slope made by each ReferencesCited UNITED STATES PATENTS Re. 22,051 3/1942 Bruce 343731 X 1,910,1475/1933 Bruce 343731 3,234,556 2/1966 Tanner 343-773 X 3,273,154 9/1966Tanner 343--773 X 3,325,815 6/1967 Jones et al. 343-739 X FOREIGNPATENTS 109,362 12/ 1931 Australia.

OTHER REFERENCES Rotman et al.: The Sandwich Wire Antenna: A New Type ofMicrowave Line Source Radiator, IRE National Convention Record, pt. I,Mar. 18-21, 1957, pp. 166472.

HERMAN KARL SAALBACH, Primary Examiner WM. H. PUNTER, Assistant ExaminerUS. Cl. X.R.

